Effect of Deposition Temperature on Properties of Undoped Ultrasonically Sprayed ZnO Thin Films

Twoanalogous sets of nanostructured ZnO thin films were deposited by Ultrasonic Spray Pyrolysis (USP) by varying the substrate temperature in the range 300 – 430 ºC, the rest of the deposition parameters being fixed. One set was deposited on glass and the other on crystalline silicon substrates. All samples were post-treated at 450 ºC for 2 hours in air. The effect of the deposition temperature on the morphological, optical and microstructural properties was analysed through five different techniques. The custom-made USP set-up was equipped with some specific features, which diminish the negative effect of convective currents and improve film homogeneity. Films with specular reflectance, good homogeneity, good adherence to substrate, high transmittance in the visible spectral range and with the typical hexagonal wurtzite microstructure were obtained. The physical properties of the films strongly depend on substrate temperature in the studied range. In particular, very smooth films at high deposition rate were deposited at 350 ºC. However, depositing at temperatures higher than around 400 ºC allowed to obtain, under high and increasing deposition rates, better crystalline quality and crystallite orientation towards the direction normal to planes (002)(c-axis oriented films), which is useful for specific applications.